Installations for reprocessing irradiated nuclear fuels are provided with what are known as large-area hot cells for receiving the process components. In such radiation-shielded cells, the process components are set up in frames or structures which are known as racks. The racks are arranged at the longitudinal sides of the cell with a transportation and handling passageway therebetween.
For the purposes of carrying out maintenance and repair operations on the process components, it has been suggested that the operations can be performed by means of movable remote-handling machines. One proposal in regard to a remote-handling system provides that a remotely-controlled travelling bridge crane operates above the racks and beneath the top wall of the cell. The crane passes over the racks and has a cable or chain lifting unit which operates vertically. Disposed beneath the travelling bridge crane is a second movable bridge carrier which has a vertical mast which is movable on a trolley. Disposed on the mast is a vertically movable chassis frame structure with an extendable arm which has a tool carrier plate for carrying or connecting the tools or handling apparatus. With this arrangement, it is possible to install a manipulator system affording the possibility of horizontal access to the process equipment from the handling passageway. In this connection, reference may be made to the journal "Atomwirtschaft", August/September 1984, pages 436 to 438, and U.S. Pat. No. 4,664,873.
A further proposal regarding the configuration of suitable remote-handling machines or carrier and positioning apparatus for remote-handling equipment or tools provides that the individual implements or machine tools are disposed in special carrier arrangements which are suitable for being picked up by a crane hook. The remote-handling implement which is suspended by its pick-up means from the crane hook is moved to the location of use thereof by means of the remote-control means of the travelling bridge crane as disclosed in U.S. Pat. No. 4,592,258.
The maintenance system with crane hook and carrier apparatus represents a lower level of complexity than the bridge carrier arrangement with the vertical guide mast which carries the manipulator systems. With the remote-handling concept consisting of the "crane hook and special receiving apparatus" it is not possible to carry out operations within the racks on such components that are located beneath other process components in the rack and that lie back from the front end of the rack. Stated otherwise, it is not possible with a cable or chain lifting unit which is positioned above the rack and which operates vertically to reach components which are beneath existing components in the rack.
The result of using the remote-handling concept consisting of the "travelling bridge crane and carrier apparatus" was that spaces were left free beneath components already present in the particular rack, and the components which were to be lifted or replaced were arranged on the outside surface of the rack in the form of a pyramid.